This invention relates to a combination type standard cell having low temperature coefficients.
As the standard cell, there have heretofore been employed saturated type standard cells (neutral cells and acidic cells) containing 10 to 12.5% of Cd amalgam. By a standard cell is meant a cell which produces a given fixed magnitude of electromotive force (voltage) to be used as a standard.
The electromotive force of a given cell varies with the temperature. The electromotive force is expressed by the following formula involving temperature coefficients. EQU E.sub.t = E.sub.20 + .alpha..sub.20 (t - 20) + .beta.(t - 20).sup.2 (For 1 volt) EQU E.sub.t = E.sub.20 {1 + .alpha..sub.20 (t - 20) + .beta.(t - 20).sup.2 } (For N volts)
wherein, E.sub.t and E.sub.20 stand for electromotive forces at temperatures of t.degree. C and 20.degree. C and .alpha..sub.20 and .beta. for primary and secondary temperature coefficients respectively.
The temperature coefficients of a standard are desirably as low as possible. In most of the standard cells which have to date been put to practical use, the temperature coefficients are on the following orders at best. EQU .alpha..sub.20 = -40 .mu.V/k EQU .beta. = -0.84 .mu.V/k.sup.2
The established practice is to place the standard cell in a bath capable of sensitive temperature control and maintain the electromotive force of this standard cell at a constant level by controlling the temperature of the bath as accurately as possible.
No matter what efforts are made, however, the temperature-control bath cannot be made absolutely free from the effect of slight changes in ambient temperature. In actual practice, therefore, it is impossible to obtain a perfectly constant electromotive force with the conventional standard cell. Need is felt, therefore, for the development of a cell having much smaller temperature coefficients.
An object of this invention is to provide a novel standard cell whose temperature coefficients are decidedly smaller than those of the conventional standard cells.